A Single-Frame Deflectometry Method for Online Inspection of Light-Transmitting Components

Abstract

Transparent materials are widely used in industrial applications, such as construction, transportation, and optics. However, the complex optical properties of these materials make it difficult to achieve precise surface form measurements, especially for bulk surface form inspection in industrial environments. Traditional structured light-based measurement methods often struggle with suboptimal signal-to-noise ratios, making them ineffective. Currently, there is a lack of efficient techniques for real-time inspection of such components. This paper proposes a single-frame measurement technique based on deflectometry for large-size transparent surfaces. It utilizes the reflective characteristics of the measured surface, making it independent of the surface’s diffuse reflection properties. This fundamentally solves the issues associated with signal-to-noise ratios. By discretizing the phase map, it separates the multiple surface reflection characteristics of transparent devices, enabling transparent device measurement. To meet the requirements of industrial dynamic measurement, this technique only needs a simple and low-cost system structure, which contains just two cameras for image capture. It does not require phase shifting to complete the measurement, making it independent of the screen and having the potential for larger surface measurement. The proposed method was used to measure a 400mm aperture automobile glass, and the results showed that it is able to achieve a measurement accuracy on the order of $10~\mu $ m. The method proposed in this paper overcomes the influence of surface reflection on transparent objects and significantly improves the efficiency and accuracy of large-sized transparent surface measurements by using a single-frame image measurement. Moreover, this method shows promise for broader applications, including measurements of lenses and HUD (Heads-Up Display) components, showcasing significant potential for industrial applications.